1. Technical Field
The present disclosure relates to a nonvolatile memory device and, more particularly, to a security apparatus and method for the nonvolatile memory device.
2. Discussion of Related Art
Nonvolatile memory devices include a mask ROM (read only memory), an EEPROM (electrically erasable and programmable ROM), an EPROM (erasable and programmable ROM), and so forth. The EEPROM that is electrically erasable or programmable has been increasingly used for system programming that requires continuous updating or as an auxiliary memory device.
More specifically, a flash EEPROM, hereinafter referred to as a flash memory device, having a higher integrity than a conventional EEPROM is very useful as a high-capacity auxiliary memory device. The flash memory device includes a NAND type, a NOR type, and an AND type. The NAND type flash memory device has a high integrity and is widely used as a data storage medium. The NOR type flash memory device has a fast data access speed and is widely used as a program code storage medium.
The nonvolatile memory device is widely used in a system demanding security and a predetermined storage device like a smart card. The system demanding security, however, is sometimes attacked by a hacker and yields confidential data. Thus, a demand for protecting the nonvolatile memory system is increasing.
The attacker obtains the data using an illegal method by analyzing the effect on a system, for example, a change in the output of the system, when a predetermined bit of data bits transmitted through a data transfer path of the system, for example, a data bus, is arbitrarily changed. To protect the nonvolatile memory from attack, conventionally, a method of repeatedly reading data and determining whether the read data is identical is used. Also, when the data is repeatedly read, the data is read through a random delay, so that the attack can be protected.
The conventional method, however, needs a plurality of data read operations and data comparisons. In addition, it is difficult to realize an ideally random delay and, to irregularly read a plurality of data, the performance of the system is deteriorated and the size of a system code such as firmware increases, which is inefficient.
Thus, a security apparatus and method is needed that can prevent the deterioration of performance due to utilizing a software protection method, that can realize an automatic protection mechanism in hardware, and that can improve the security performance of a system or chip, as well as the overall performance of the system.